1. Field of the Invention
The invention relates to processes for preparing fluoroalkyl organosilicon compounds by reacting fluorine-containing olefins with organosilicon compounds in the presence of a platinum catalyst.
2. Discussion of the Background
In recent years, a large number of new applications have been discovered for fluoroalkylchlorosilanes and fluoroalkylalkoxysilanes. These compounds are useful as surfactants to modify the surfaces of lenses and optical fibers or for producing oil-, dirt-, and water-repellent surfaces, as lubricants, as primers for fluoro resins, as ingredients in cosmetic preparations, and as modifiers in fluoro-rubbers and silicone rubbers.
Platinum catalysts are often used for hydrosilylation reactions of fluoroolefins to produce the above-mentioned silanes. Typically, the preferred catalysts are those in which platinum is in the (+4) oxidation state. However, these Pt(IV) catalyst systems suffer from a number of disadvantages.
In many cases, the reactions are required to run under a closed system. JP 02 178 292 A2 discloses the reaction of F.sub.3 C(CF.sub.2).sub.2 C(CF.sub.3).sub.2 CH.sub.2 CHCH.sub.2 with HSiCl.sub.3 in a blown glass tube in the presence of a H.sub.2 PtCl.sub.6 catalyst at a temperature of 100.degree. C. for 3 h with a yield of 83%. EP 0 538 061 A2 discloses a reaction of CF.sub.3 CF.sub.2 CF.sub.2 OCF(CF.sub.3)CF.sub.2 OCF.sub.2 CF.sub.2 CHCH.sub.2 with CH.sub.3 SiHCl.sub.2 in the presence of H.sub.2 PtCl.sub.6 in a steel autoclave at a reaction temperature of 120.degree. C., with a reaction period of 20 h and a resulting yield of 67%.
At atmospheric pressure, such reactions are relatively lengthy. For instance, JP 06 239 872 A2 discloses a reaction time of 48 h for the reaction of C.sub.3 F.sub.7 O[CF(CF.sub.3)CF.sub.2 O].sub.3 CF(CF.sub.3)CHCH.sub.2 with (CH.sub.3).sub.3-n SiHCl.sub.n (n=1,2) in the presence of H.sub.2 PtCl.sub.6 at a reaction temperature of 150.degree. C., resulting in a yield of 88%. WO 94/20442 discloses a yield of 89% and a reaction period of 50 h for a hydrosilylation reaction, at a reaction temperature of 100.degree. C. in the presence of H.sub.2 PtCl.sub.6.
The reactions may not be stereospecific. WO 94/20442 additionally discloses that, for example, in the hydrosilylation reaction of p-CF.sub.3 C.sub.6 H.sub.4 CHCH.sub.2 with CH.sub.3 SiHCl.sub.2, isomerization may occur with a concomitant reduction in selectivity. In this case, an 87:13 ratio of .beta.-silylated to .alpha.-silylated fluoroolefin is obtained with a yield of 89%.
To raise the selectivity and reactivity, and in some cases to improve the solubility of the platinum compound, complexing reagents are added to the platinum catalyst. For example, JP 03 106 889 A2 teaches the addition of acetone. EP 0 466 958 A1 discloses isopropanol as an additive, while EP 0 573 282 A1 discloses the use of H.sub.2 PtCl.sub.6 in 2-ethylhexanal. It is also known to add m-xylene hexafluoride to the Pt catalyst (EP 0 573 282 A1). However, in all of these examples, the cost and complexity of preparation are considerable.
In general none of the above-mentioned catalyst systems are sufficiently reactive or selective, with the result that, from an economic standpoint, such processes are of little interest for the preparation of fluoroalkyl-containing organosilicon compounds.